At large accelerators, bent crystals are employed to deflect weakly divergent proton beams at the stages of extraction and collimation. We demonstrate that a divergent particle beam may be ...efficiently deflected using a crystal with a focusing entry face. A 180 GeV/c pion beam with divergence near 0.060 mrad, which exceeds the Lindhard angle by a factor of 4, has been experimentally deflected by 0.25 mrad with efficiency near 22%. The proposed focusing crystal may serve as an element of a novel particle optics for secondary-particle beams in the TeV energy region.
Recently studies are started on the application of volume reflection of particles in crystals for the steering beams (for extraction and collimation of a circulating beam in accelerators). Volume ...reflection is more efficient than channeling, but requires amplification of the deflection angle by applying multicrystals. The report discusses two new applications of multicrystals made like multistrip structures: (i) the property of effective deflection of particle beam was used to protect the septum magnets of the U-70 in the process of extraction of the proton beam with energy of 50 GeV; (ii) the possibility of generation of gamma radiation was studied in the secondary electron beam with energy of 7 GeV. In both cases, promising preliminary data were obtained.
The ordered positions of atoms in crystals give a reason to study multiple Coulomb scattering of high energy charged particles within them. In addition, the accurate representation of multiple ...scattering of high energy protons in a bent crystal is important for studies of crystal assisted collimation at the SPS and the LHC. Multiple scattering of 400GeV/c protons in bent silicon crystals was measured for orientations far from the directions of main crystallographic planes and axes in conditions excluding channeling of protons. The observed RMS widths of the angular distributions are a little larger than those obtained from the Moliere theory. Simulation of multiple scattering in a model of binary collisions with the crystal atoms shows about 3.5% decrease of the RMS deflection with respect to the model of a sequence of random collisions. We consider this as a possible indication of a reduction of multiple scattering of protons in a crystal in comparison with its amorphous state.
The effect of multiple volume reflections in one crystal was observed in each of several bent silicon strips for 400GeV/c protons. This considerably increased the particle deflections. Some particles ...were also deflected due to channeling in one of the subsequent strips. As a result, the incident beam was strongly spread because of opposite directions of the deflections. A modified multi-strip deflector produced by periodic grooves on the surface of a thick silicon plate was used for these measurements. This technique provides perfect mutual alignment between crystal strips. Such multi-strip deflector may be effective for collider beam halo collimation and a study is planned at the CERN SPS circulating beam.
Recent discussions about accelerators in high energy physics identified several challenges for the future, where it is necessary to focus particle beams over a distance of a few cm. In this paper, we ...investigate the focusing of particles by a new crystal device having such a capability. The trajectories of 180 GeV/c pions passing through a 500 µm thick focusing crystal were reconstructed using silicon microstrip detectors. It is shown that a parallel beam of particles can be focused in one plane at a distance of 15.5 cm from the crystal, in a narrow line with an rms width of 8 µm.
Bent silicon crystals in channeling mode are already used for beam extraction and collimation in particle accelerators. Volume reflection of beam particles is more efficient than beam channeling; ...however, the mean deflection angle is rather small. An experiment on the deflection of a 400 GeV/
c
proton beam and a 150 GeV/
c
π
−
beam at CERN using a multi-strip silicon deflector in reflection mode is described. The mean deflection angle of beam particles has been considerably increased due to sequential volume reflections realized in the deflector. This gives possibility for a successful usage of the multi-strip deflectors for beam collimation in high-energy accelerators.
Two high-accuracy goniometers equipped with two bent silicon crystals were installed in the betatron cleaning insertion of the CERN Large Hadron Collider (LHC) during its long shutdown. First beam ...tests were recently performed at the LHC with 450 GeV/c and 6500 GeV/c stored proton beams to investigate the feasibility of beam halo collimation assisted by bent crystals. For the first time channeling of 6500 GeV/c protons was observed in a particle accelerator. A strong reduction of beam losses due to nuclear inelastic interactions in the aligned crystal in comparison with its amorphous orientation was detected. The loss reduction value was about 24. Thus, the results show that deflection of particles by a bent crystal due to channeling is effective for this record particle energy.
Strong reduction of multiple scattering for channeled particles has been observed in an experiment on the deflection of a 180 GeV/c π+-meson beam by bent silicon crystals. The RMS deflections due to ...multiple scattering for the channeled particles were about six times smaller than for non-channeled ones. It was shown that the approach suggested recently for the description of multiple scattering for channeled particles using the experimental data for random crystal orientations gives fair agreement with the experiment.
Currently, for extraction and collimation of proton beam at the large accelerators bent silicon single crystals are used. Recently the new device for multiple deflection of the proton beam was ...developed, it consists of several bent strips of silicon in the reflection mode. In the device the successive bending of silicon strips at the surface of a thick plate is achieved due to internal stresses in the material of the crystal due to the Twyman effect as a result of applying mechanical grooves. Method of X-ray topography at synchrotron radiation with angular scanning was applied for measurement of bending of the individual strips of the deflector and the crystal as a whole. The results of the measurement are compared with the results obtained in the proton beam.
Channeling efficiency in a target-crystal assembly Scandale, W.; Cerutti, F.; Esposito, L.S. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
03/2020, Letnik:
467
Journal Article
Recenzirano
In view of possible future fixed target experiments requiring precisely steered charged particle beams, the UA9 Collaboration has undertaken experimental studies of the use of bent silicon crystals ...for this purpose. The channeling efficiency of positively charged particles inside the crystalline lattice has been investigated in detail for a setup with a tungsten target installed in front of the crystal. Due to multiple Coulomb scattering inside the target, the channeling efficiency was observed to be reduced by a factor of about 6.1 for a 180 GeV/c quasi-parallel hadron beam. The yield of nuclear interaction secondaries as an estimation of the additional machine background is also discussed.
PDF
